1. Field of the Invention
The present invention relates to a color processing method and apparatus.
2. Description of the Related Art
If a recording apparatus uses, for example, cyan (C), magenta (M), yellow (Y), and black (K) recording materials such as ink or toner, R, G, and B image data is color-separated into C, M, Y, and K data corresponding to the individual recording materials in image processing for generating print data. The color separation processing is typically performed using a lookup table (LUT). The LUT defines a method of generating C, M, Y, and K data by combining recording materials on the basis of the combination of R, G, and B data.
In the print industry where ink and toner are used, a particular color is sometimes used in a recording apparatus so as to enlarge the reproducible color gamut of the recording apparatus, that is, so as to accurately reproduce color saturation. In this case, in addition to the usually used cyan, magenta, and yellow (basic colors) and black color materials, red, orange, green, blue, and violet recording materials are also used.
Japanese Patent Laid-Open No. 2001-136401 discloses a color separation technique in which a color gamut is separated into color sub-gamuts each composed of black and three chromatic colors so as to extract the combination of the colors from each color sub-gamut. However, in this technique, the combination of colors is extracted from a color sub-gamut composed of four colors, therefore, it is limited to the combination of four or less colors and to the combination having been determined when the color sub-gamut was generated. Accordingly, appropriate color separation over the entire color gamut cannot be achieved. In addition, smooth gradation cannot be maintained at boundaries between color sub-gamuts.
In Japanese Patent Laid-Open No. 2003-011432, if the color saturation of a particular color used to represent a particular color hue becomes lower than that of the mixture of basic colors in a certain lightness region, color separation is performed using both the particular color and the basic colors. For example, if green ink having high lightness is used to represent a green hue, the color mixture of cyan and yellow is used in the low lightness region of the green hue so as to enlarge the color gamut. However, this method can enlarge the color gamut of a particular color hue, but cannot enlarge the color gamut of a basic color hue.
Japanese Patent Laid-Open No. 2005-059360 discloses a technique for enlarging a color gamut of a basic color hue by using a complementary color of a particular color in the low lightness region of the basic color hue. However, this technique focuses on just high lightness and high color saturation of a particular color. It is doubtful that a color gamut can be enlarged sufficiently by using the technique. In addition, the use of a complementary color of a particular color is undesirable from a granularity viewpoint.